Digital transmission in an analog domain such as video, audio, and microwave frequencies occur serially in time. One such example is teletext data in video transmission.
Teletext transmissions occur at frequencies and/or data rates which are generally known to the receiver. However, during teletext transmission the transmission frequencies can change due to line length variations and/or due to incorrect frequency generation. In addition, during teletext transmission, the terrestrial transmission deteriorates the shape of the analog signal and can be difficult to extract exact digital data, as the sampled analog signal can be in the transition of teletext data bits. For proper detection of teletext data, a prior knowledge and/or accurate estimation of data rate/bit width is required. Further, even if correct estimation of data rate is known in some instances, variations during transmissions can cause errors in detection of frequencies of transmission.
In such situations, the teletext decoder estimates the transmission frequency and passes it on to a detection module. Errors resulting from such estimation of transmission frequencies can require expensive and highly complex decoders, that rely on clock generation synchronized to the teletext data rate and/or phase locked loops that are capable of locking onto the initial synchronizing pattern of the teletext signals, to decode the teletext data.